The present invention relates to apparatus and methods for determining when equipment is clean. More particularly, the invention relates to such apparatus and methods which involve electrical conductivity measurements and which preferably provide a signal indicating that the equipment is clean.
Throughout the process industries, process effectiveness and efficiency often requires that equipment be maintained at a high degree of cleanliness. Thus, in many situations, pieces of equipment, such as processing vessels, heat exchangers, storage tanks, pipelines and the like, are subjected to regular and routine cleaning procedures to remove debris and/or contaminants from the equipment, for example, the internal components or surfaces of the equipment.
Quite often a visual inspection of the equipment after the cleaning procedure is sufficient to determine that the equipment is acceptably clean. However, there are instances where such a visual inspection is not a satisfactory indication of equipment cleanliness. Examples include equipment used in the biotechnology, pharmaceutical and related industries which are regulated at least to some extent by the U.S. Food and Drug Administration, hereinafter the FDA.
With regard to certain pieces of equipment, the FDA has mandated that the equipment pass a certain test before it is certified as being clean, and, therefore, ready or eligible to be employed or operated again, e.g., in a manufacturing process. In brief, this FDA mandated test requires that the equipment be subjected to rinsing with highly pure water, e.g., ultra-pure water. The electrical conductivity of the effluent rinse water is monitored. In order for the equipment to be certified clean in accordance with this test procedure, the electrical conductivity of the effluent rinse water must be at or below a predetermined value, for example, at or below 1.0 microsiemen per square cm.
One problem with this test is that it frequently provides false negative results, that is it frequently indicates that clean equipment is not clean. Such false negative results can lead to prolonged and unnecessary process downtime while the equipment is subjected to re-cleaning. An important reason or cause of this problem is believed to be the purity of the high purity rinse water itself, which often varies over a relatively wide range. Thus, in order to obtain certification that a piece of equipment is clean, it is often necessary to wait until the high purity rinse water has been sufficiently processed so as not to unduly contribute to the conductivity of the effluent rinse water. This, in turn, can result in processing delays and, ultimately, to increased manufacturing costs.
It would be advantageous to provide a new system for determining that a piece of equipment is clean.